(a) Field of the Invention
The present invention relates to a D2D communications system and a D2D communication method, using a non-licensed band as an auxiliary band, and more particularly, to a D2D communications system and a D2D communication method, using a non-licensed band as an auxiliary band while allocating frequency resources which will be used for D2D communications between terminals sharing up and down frequency resources of a cellular network.
(b) Description of the Related Art
Device-to-device communications indicate direct communications between terminals that are locally adjacently located without using an infrastructure including base stations, and development and standardization of D2D communications techniques using licensed frequency bands have been in progress.
In a cellular system, when terminals located in an adjacent distance perform D2D communications, a base station may disperse loads, and the D2D terminals perform short-distance transmission, which reduces not only terminal power consumption but also transmission delay. Further, in terms of the whole system, conventional cellular terminals and the D2D terminals spatially re-use frequencies by sharing the same frequencies, thereby improving a frequency-using efficiency. In addition, the D2D communications may be used for relays between terminals, and are expected to generate new proximity-based services such as for collecting information related to stores and thinks located within an adjacent distance, for precise indoor measurement, for group communications between persons located within the adjacent distance, for network games, for location-based advertisements, or disaster communications.
Allocation of resources to be used in a D2D communications link is generally performed by selecting a resource that is least interfered from a cellular link while preventing performance deterioration of the cellular link. This allocating method is performed in a base station in a centralized type, and requires channel information of terminals and distance information. For example, according to an allocating method, D2D terminals located outside of the cell may use resources of a cellular terminal that is located sufficiently distantly from the D2D terminals.
However, according to such an allocating method, it is difficult to securely acquire channels through a resource-allocating algorithm since the allocating method does not consider scheduling variations and mobility of the cellular terminal. Besides, overhead may be generated in the whole system in the case of a D2D resource allocating method that adaptively re-allocates resources depending on a resource-allocating variation of the cellular terminal.
Accordingly, measures are required to prevent performance deterioration of the D2D terminals depending on terminal mobility, thus-channel variation, and resource-allocating scheduling variation in the resource allocation of cellular network based D2D communications techniques.
Background techniques of the present invention were disclosed in Korean Patent Laid-Open Publication No. 10-2014-0080298 (2014.06.30).